It is proposed in the United States that certain sizes of trucks be required to comply with emission standards. For example, there are proposals that model year 1987, medium weight, heavy duty trucks be required to meet an emission standard Medium weight, heavy duty trucks are trucks which have a gross vehicle weight in a range of 8,500-14,000 pounds. Such trucks normally operate on interstate highways, carrying goods between distant cities. This size truck is usually equipped with an internal combustion engine, burning a hydrocarbon fuel such as gasoline. These vehicles operate at normal throttle conditions during a substantial portion of their cycle but, in many instances, these vehicles are required to advance to a wide-open throttle condition, obtaining maximum output from the internal combustion engine. Such wide-open throttle excursions are encountered during acceleration of the truck to highway operating speeds and accelerations caused for passing other vehicles.
When such medium weight, heavy duty trucks are operated at wide-open throttle conditions, the engines are generally operating at an air/fuel ratio in a range of 12-13 during maximum load conditions. In such an operating air/fuel ratio, an engine of this type will produce an exhaust gas mixture which is very hot, approximately 1600.degree. F. The exhaust gases so-produced are also rich in oxides of nitrogen because of the range of air/fuel ratios, and will contain approximately 5-6 mole percent of carbon monoxide. It is known that a complete oxidation of every mole percent carbon monoxide produces about 180.degree. F. rise in temperature. Therefore, if exhaust gases containing 6 mole percent carbon monoxide are oxidized by passing them over an oxidation catalyst alone, the maximum exhaust gas temperature that could be generated on the exhaust gas catalyst could approach a temperature of 2600-2700.degree. F., assuming no loss of heat. Such an extremely high temperature, of course, is detrimental to the catalyst materials and catalyst substrates. It would not take long for a vehicle having a catalyst operating at such a high temperature to deteriorate severely and deactivate the catalyst system.
The primary purpose of our invention is to provide a method of operating a catalyst system for a medium weight, heavy duty truck which provides excellent control for carbon monoxide, unburned hydrocarbons and oxides of nitrogen, but yet does not produce undesirably high temperatures over the oxidation catalyst used in the system. The method of our invention is also one which readily handles the reduction of oxides of nitrogen at wide-open throttle conditions when the maximum amount of such oxides of nitrogen are being generated in the internal combustion engine associated with the medium weight, heavy duty truck. Also, during these maximum load conditions, our method provides for approximately 100% oxidation of unburned hydrocarbons and provides 80-95% oxidation of carbon monoxide. Under partial throttle conditions or normal throttle conditions, almost complete oxidation of carbon monoxide and unburned hydrocarbons is achieved, and the amount of oxides of nitrogen produced is very reduced because the engine is running under less than full load conditions, whereat the oxides of nitrogen generated by the burning process in the engine is substantially reduced in and of itself.
A search was carried out on the subject matter of this specification in the U.S. Patent and Trademark Office. As a result of this search, a number of U.S. patents were cited. In our opinion, none of the patents either disclosed or suggested the system which is to be disclosed and claimed herein. However, a brief review of these patents is set forth below for the purpose of setting the state of the art.
U.S. Pat. No. 3,045,422, issued on July 24, 1962, for "Temperature Control of a Catalytic Exhaust Purifier." This patent shows air delivery upstream of a catalyst, controlled in a manner so as to keep the catalyst temperature within its operating range. The control is also carried out so that the air/exhaust gas weight ratio decreases as the engine speed increases.
U.S. Pat. No. 3,086,353, issued on Apr. 23, 1963, for "Afterburner Systems." This patent shows a system in which fresh air supplied to an afterburner is controlled to limit the temperature to which the afterburner may rise. Control of the temperature is based upon measurements of the afterburner temperature.
U.S. Pat. No. 3,826,089, issued on July 30, 1974, for "Air-Pollution Preventive Arrangement." This patent teaches a system in which the proportion of air supplied to an thermal reactor and a catalytic converter is regulated in accordance with the air/fuel ratio to secure a high recombustion efficiency throughout varying engine operating modes.
U.S. Pat. No. 3,869,858, issued on Mar. 11, 1975 for "Exhaust Gas Purifying System for Motor Vehicles." In the system shown in this patent, a flow control valve, which is operable in response to a warm-up condition, acceleration condition or other operating condition of the engine, is used to supply secondary air, selectively to either a reduction treatment device or oxidation treatment device which are installed in the exhaust system for treating exhaust gases.
U.S. Pat. No. 3,908,365, issued on Sept. 30, 1975, for "Treatment of Gaseous Effluent." This patent teaches the treatment of effluent arising from incomplete combustion of a hydrocarbon fuel by a process which includes the sequential steps of oxidizing a portion of the total oxidizable components, lowering the oxides of nitrogen content in the effluent by chemical reduction at an elevated temperature, and further oxidizing the remaining oxidizable components in the effluent to an acceptable level.
U.S. Pat. No. 3,919,842, issued on Nov. 18, 1975, for "Controller for Proportional Control of Reducing Converter Air." This patent teaches a controller in an exhaust emission control system for an engine of an automotive vehicle which controls secondary air flow between a region ahead of a reducing converter and a region intermediate the reducing converter and an oxidizing converter. The amount of air introduced ahead of the reducing converter is proportional to engine exhaust flow and is preferably introduced closely adjacent to the exhaust ports of the engine.
U.S. Pat. 3,943,711, issued on Mar. 16, 1976, for "Multi-Stage Air Pump for Supplying Secondary Air to an Exhaust Gas Purification System." This patent discloses a plurality of pump elements for progressively increasing the pressure of air to supply, respectively, air at various pressures into portions in an exhaust gas purifying system requiring secondary air.
U.S. Pat. No. 4,098,078, issued on July 4, 1978, for "Process and Apparatus for After-Burning of Combustible Pollutants from an Internal Combustion Engine." This patent discloses a pump which supplies an air feed to an exhaust manifold and to a catalytic reactor, with an automatic control of the air injection ratio.
U.S. Pat. No. 4,147,030, issued on Apr. 3, 1979, for "Engine Exhaust Gas Purification System." This patent discloses an engine exhaust gas purification system having an exhaust gas reactor mounted on the engine exhaust pipe, a secondary air supply system having a secondary air supply passage connected to the exhaust pipe upstream of the reactor, and an exhaust gas air/fuel ratio detector mounted on the exhaust pipe to detect air/fuel ratio of the exhaust gases in the exhaust pipe. A secondary air supply control valve is provided in the secondary air supply passage and controlled by a valve actuator having a diaphragm to which positive pressure of the secondary air and engine intake vacuum pressure can be applied. The application of the positive and vacuum pressure to the diaphragm is controlled by solenoid valves which are controlled in accordance with the air/fuel detector output voltage which represents the detected exhaust gas air/fuel ratio, whereby the secondary air supply control valve is controlled such that the secondary air is supplied to the engine exhaust gases at a continuously controlled, variable rate.
U.S. Pat. No. 4,299,089, issued on Nov. 10, 1981, for "Secondary Air Control System in an Internal Combustion Engine." This patent teaches a secondary air system which delivers air to an exhaust manifold and upstream of an oxidizing converter. The secondary air system is computer controlled in response to vacuum, intake air temperature and air flow.
U.S. Pat. No. 4,342,194, issued on Aug. 3, 1982, for "Electric Air Controlled Switching Valve." The electrical air controlled switching valve is used for controlling the delivery of secondary air from an engine driven air pump selectively, as a function of both engine operation and the operation of an associated emission control system, to either the exhaust manifold of an engine, preferably at a location closely adjacent the exhaust ports of the engine, during low temperature engine operation, to the atmosphere, as at the dirty side of the air cleaner associated with the induction system of the engine, during low temperature engine deceleration, to a converter in the exhaust system for the engine downstream of the exhaust manifold during normal engine operation, or again to the atmosphere, as at the dirty side of the air cleaner, when the converter temperature exceeds a predetermined temperature.
U.S. Pat. No. 4,358,927, issued on Nov. 16, 1982, for "Pressure Operated Proportional Air Management Valve." The air management valve is one in an exhaust emission control system for an engine of an automotive vehicle. The valve is operated to control, selectively, secondary air flow to the exhaust manifold next adjacent to the exhaust ports of the engine, to the center of a dual bed catalytic converter, and to the atmosphere.